Manufacture of artificial silk

ABSTRACT

Artificial silk spun on unyielding perforated bobbins is washed and after-treated, e.g. desulphurized, by the pressure or suction method using the perforations, and then, prior to drying, the perforations are rendered ineffective so as to prevent moisture from escaping through them.  By this means irregularities caused by uneven contractions are avoided.  The perforations may be rendered ineffective by closing the bobbins at the ends, or a number of bobbins may be superposed to form a column and the column closed, or the bobbins may be slid on a tube, or the inner surface of the bobbin may be covered by fitting an elastic sleeve. If desired, the drying of the artificial silk may be interrupted prematurely, e.g., when the water content is about 15, 20, or 25 per cent.

Patented June 2, 1936 UNITED STATES ATEN'E' QFFICE MANUFACTURE OF ARTIFICIAL SILK Main, Germany No Drawing. Application March 8, 1934, Serial No. 714,722. In Germany March 14, 1933 2 Claims.

Our present invention relates to the manufacture of artificial silk and more particularly to drying artificial silk.

One of its objects is an improved process of 5 drying artificial silk spun on perforated bobbins. Further objects will be seen from the detailed specification following hereafter.

Artificial silk produced by the wet spinning process and wound on perforated bobbins, is generally washed by passage of the treating liquid through the perforations under suction or pressure, and subsequently dried on the spinning bobbins. However, when drying the wet bobbins in the usual manner by exposing them to a current of air impinging upon them from all directions, an artificial silk is obtained which shows great differences in its dyeing and mechanical properties accordingly as it formed the beginning, the middle or the end of the winding on the bobbin. The differences are due to the fact that while the wet swollen silk dries, it not only tends to become diminished in thickness, but also to become considerably shorter, this being realized to some extent in the inner layers of the winding, but is prevented at both ends thereof. The after-treatment of the silk in hank-form compensates but imperfectly for the differences in quality due to these causes.

For obtaining a more uniform product it has already been proposed to enwrap the wound bobbins prior to drying them in envelopes which are impervious to moisture. By this expedient the moisture contained in the wet silk can escape only through the perforations towards the interior of the bobbin. By repeating this treatment after rewinding the silk on a second bobbin and rewetting it, the thread may be made uniform to a great extent throughout its length. This process, however, cannot be practiced on a commercial scale because of the costs of handling the bobbins twice for fitting the impervious envelopes and of rewinding the thread.

According to the invention, the same effect may be produced in a much simpler way by preventing the moisture from escaping through the perforations towards the interior of the bobbin and forcing it to escape exclusively through the outer surface of the winding. To this effect, the bobbins may for instance be closed at their both ends, or a number of bobbins may be superposed in known manner to form a column of bobbins and the ends of the column may be closed, or the bobbins may be slid on a tube, the external diameter of which is approximately the inner diameter of the bobbin, or the inner surface of the bobbin may be covered by fitting an elastic sleeve; briefiy, there may be used any means by which the perforations are closed and a perforated bobbin is transformed in a certain degree into a nonperforated one. Generally speaking any means is used and lies within the scope of the invention which causes drying to be started at the outer layers of the Winding and to be progressively carried towards the interior layers, so that the outer layers of threads are dried first, whereas the layer of threads lying directly on the bobbin is dried last.

The uniformity of the different portions of a hank of threads as to their dyeing properties may be still further improved and ensured by interrupting the drying operation prematurely, that is to say before the winding of thread is dried throughout. When drying is conducted for instance in an atmosphere having a relative content of moisture of 25 to 30%, a silk is obtained which, when perfectly dry, contains 6 to '7 grams of water per grams of dry cellulose hydrate. According to the invention drying is interrupted prior to obtaining this content of water, for instance at a content of water of say 15, 20 or 25 per cent. It must in any particular case be ascertained by experiment how far the drying must be carried in order to obtain the best effect possible, the optimum effect depending principally on the kind of silk employed, on the thickness of the winding of threads and on the method of operation of the dryer. By interrupting prematurely the drying operation it is ensured that the innermost layers of the winding of thread contain appreciably more moisture than the outermost and intermediate layers and thus are but slightly liable to shrinking. As it is known, the properties of artificial silk in respect of being uniformly dyed and the mechanical properties are the more impaired, the more the tendency to shrinking is promoted by a progressive drying of the winding.

The essence of the invention therefore is the drying of a winding of threads only from the outer surface of the winding towards the support of the winding in such a manner that the innermost layers of the winding are less dried than the outer layers thereof.

The following examples illustrate the invention:-

Example 1.A winding of wet viscose silk, spun in a so-called Muller II bath containing sulfuric acid and sodium sulfate, and wound on perforated bobbins, is washed free from acid by the suction or pressure method and then contains so much moisture that 315 grams of wet fibers correspond with 100 grams of dry cellulose. The bobbins are then dried with air having a relative content of moisture of 30 per cent at a temperature of between and C. while closing the perforations in one of the aforesaid manners until the winding contains 16 to 18 per cent of moisture and grams of dry cellulose weighing 116 to 118 grams. After having been kept for some time in a moistening room, the silk is twisted at an atmosphere having a high content of moisture on twisting machines in which there are several rows of bobbins one above the other and further treated in the usual way.

Example 2.-Viscose silk spun in a spinning bath containing sulfuric acid, sodium sulfate and magnesium sulfate, and wound on perforated bobbins, is washed free from acid by the suction or pressure method, and then has a wet weight of about 260 gramscalculated on 100 grams'of dry cellulose, and is dried, while closing the perforations, at a temperature of between 40 and 60 C. with air having a relative content of moisture of 60 per cent, until the winding contains 25 per cent of moisture or a weight of about grams per 100 grams of dry cellulose. The further treatment is as described in Example 1.

The process may be applied with advantage in all cases where awet fiber is collected on a solid, unyielding and perforated support and where drying produces a considerable shrinking of the thread both in a longitudinal and a lateral direction.

It has also been the practice in the making of artificial silk to spin on unperforated bobbins, to wash the acid silk by immersing it in water or by spraying with water and to dry it afterwards; drying, therefore, has already been performed on unperforated bobbins without observing that this kind of drying presents an advantage for the dyeing properties of the silk. According to the invention, however, use is made of perforated bobbins. In this way all the advantages involved by the use of this kind of bobbins, i. e. washing and after-treatment with desulfurizing, bleaching and preparation agents by the suction and pressures method the possibility of giving the windings of thread a greater thickness etc. are combined with the advantages in respect of the dyeing properties of the silk that are obtained in drying on non-perforated bobbins.

What we claim is:-

1. In the process of spinning artificial silk the steps which comprise winding artificial silk on perforated bobbins, treating the silk on said bobbins with liquid by forcing the liquid through the silk and the perforations, and drying the silkwhile closing the perforations so that all the moisture evaporates through the outer layers of the winding of fibers.

2. In the process of spinning artificial silk the steps which comprise winding artificial silk on perforated bobbins, treating the silk on said bobbins with liquid by forcing the liquid through the silk and the perforations, drying the silk while closing the perforations so that all the moisture evaporates through the outer layers of the fiber lap, and interrupting drying prematurely so that the silk contains about 25 per cent of moisture.

EMIL HUBERT. ARNO MATTI-IES. 

